feat: flexible meal planning wizard — plan 1 meal, 1 day, several days, or a week

Backend:
- migration 005: expand menu_items.meal_type CHECK to all 6 types (second_breakfast, afternoon_snack, snack)
- ai/types.go: add Days and MealTypes to MenuRequest for partial generation
- openai/menu.go: parametrize GenerateMenu — use requested meal types and day count; add caloric fractions for all 6 meal types
- menu/repository.go: add UpsertItemsInTx for partial upsert (preserves existing slots); fix meal_type sort order in GetByWeek
- menu/handler.go: add dates+meal_types path to POST /ai/generate-menu; extract fetchImages/saveRecipes helpers; returns {"plans":[...]} for dates mode; backward-compatible with week mode

Client:
- PlanMenuSheet: bottom sheet with 4 planning horizon options
- PlanDatePickerSheet: adaptive sheet with date strip (single day/meal) or custom CalendarRangePicker (multi-day/week); sliding 7-day window for week mode
- menu_service.dart: add generateForDates
- menu_provider.dart: add PlanMenuService (generates + invalidates week providers), lastPlannedDateProvider
- home_screen.dart: add _PlanMenuButton card below quick actions; opens planning wizard
- l10n: 16 new keys for planning UI across all 12 languages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/features/home/home_screen.dart

@@ -16,6 +16,8 @@ import '../../shared/models/meal_type.dart';
 import '../../shared/models/menu.dart';
 import '../diary/food_search_sheet.dart';
 import '../menu/menu_provider.dart';
+import '../menu/plan_date_picker_sheet.dart';
+import '../menu/plan_menu_sheet.dart';
 import '../profile/profile_provider.dart';
 import '../scan/dish_result_screen.dart';
 import '../scan/recognition_service.dart';
@@ -126,6 +128,8 @@ class HomeScreen extends ConsumerWidget {
                   ],
                   const SizedBox(height: 16),
                   _QuickActionsRow(),
+                  const SizedBox(height: 8),
+                  _PlanMenuButton(),
                   if (!isFutureDate && recommendations.isNotEmpty) ...[
                     const SizedBox(height: 20),
                     _SectionTitle(l10n.recommendCook),
@@ -1641,6 +1645,68 @@ class _ActionButton extends StatelessWidget {
   }
 }
 
+// ── Plan menu button ──────────────────────────────────────────
+
+class _PlanMenuButton extends ConsumerWidget {
+  const _PlanMenuButton();
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final l10n = AppLocalizations.of(context)!;
+    final theme = Theme.of(context);
+
+    return Card(
+      child: InkWell(
+        onTap: () => _openPlanSheet(context, ref),
+        borderRadius: BorderRadius.circular(12),
+        child: Padding(
+          padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 14),
+          child: Row(
+            children: [
+              Icon(Icons.edit_calendar_outlined,
+                  color: theme.colorScheme.primary),
+              const SizedBox(width: 12),
+              Expanded(
+                child: Text(
+                  l10n.planMenuButton,
+                  style: theme.textTheme.titleSmall,
+                ),
+              ),
+              Icon(Icons.chevron_right,
+                  color: theme.colorScheme.onSurfaceVariant),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+
+  void _openPlanSheet(BuildContext context, WidgetRef ref) {
+    showModalBottomSheet<void>(
+      context: context,
+      isScrollControlled: true,
+      useSafeArea: true,
+      builder: (_) => PlanMenuSheet(
+        onModeSelected: (mode) {
+          final lastPlanned = ref.read(lastPlannedDateProvider);
+          final defaultStart = lastPlanned != null
+              ? lastPlanned.add(const Duration(days: 1))
+              : DateTime.now().add(const Duration(days: 1));
+          showModalBottomSheet<void>(
+            context: context,
+            isScrollControlled: true,
+            useSafeArea: true,
+            builder: (_) => PlanDatePickerSheet(
+              mode: mode,
+              defaultStart: defaultStart,
+            ),
+          );
+        },
+      ),
+    );
+  }
+}
+
 // ── Section title ─────────────────────────────────────────────
 
 class _SectionTitle extends StatelessWidget {